The invention relates to a method and apparatus of mining a desired geological stratum from surrounding undesired geological strata, the desired and undesired strata having different properties, especially different light reflecting properties. In the mining of coal and other valuable geological strata which occur in laminar fashion (seams), it is desirable to recover as much as possible of the valuable stratum without excessive contamination from the adjacent undesired stratum. Conventionally, this is accomplished by the operator himself. The operator of a mining maching periodically steers it in the direction of the boundary between the desired and undesired strata until contact is made with the undesirable stratum, which contact can be observed by noting the appearance of the mined product. The operator then backs the mining machine off a few inches and proceeds. Such a procedure is practical where the operator can see when contact has been made.
There are many situations when it is not practical for the operator to visually observe the mining operation. In many situations, for safety reasons, it is undesirable for an operator to be within sight of the mining face. In some situations, the stratum immediately above the desired stratum is unstable, and it is necessary to leave some of the desirable stratum in place to support the unstable stratum. Also, with auger-type mining machines and the like where an operator is stationed at a point remote from the mining face, it may be several minutes before the operator, by observing the appearance of the mined product, can tell that contact with the undesired stratum has been made, and this can result in excessive contamination of the mined material.
Devices have been constructed to indicate to the operator that the undesired stratum has been contacted so that the operator need not rely on visual inspection. One such device is shown in U.S. Pat. No. 3,333,893. In such device, the difference in the reflectivity between the desired stratum (coal) and the undesired stratum is utilized to provide an indication of when the undesired stratum has been reached. An auxillary cutting tooth is provided that operates at a fixed distance beyond the periphery of the cutting head for the mining machine itself. In practice, this distance cannot exceed about one-half inch, and the mining machine can only depart from its desired path by this fixed distance before the main cutting elements of the mining machine encounter the adjacent stratum. Utilizing such a structure which determines when the undesired stratum has actually been contacted, if the line of demarcation between the desired and undesired strata is irregular (as is usually the case), the operator has very little time to react and alter the course of the mining machine to remain entirely within the desired stratum. Also, since the auxillary cutting tool must operate at the head of the mining machine, and often contacts the rough, harsh, undesired stratum for significantly long periods of time, wear of the auxillary cutting tool is excessive, and worn bits must be replaced quite frequently.
There have also been other proposals for measuring the distance between the mining machine and the boundary of the undesired stratum, but normally such devices are based on the "back-scattering" of radioactive rays, such devices being bulky and dangerous for an inexperienced operator.
According to the present invention, a method and apparatus have been provided that minimize or eliminate all of the drawbacks inherent in the prior art. According to the present invention, it is possible to measure the distance from the mining machine to the extremity of the stratum being mined, and this can be accomplished utilizing a tool a having increased wear-life compared to the prior art, and in a simple and safe manner, using the difference between the light reflecting properties of the desired and undesired strata to indicate the distance from a reference to the undesired strata.
According to one aspect of the present invention, a method of mining a desired geological stratum from surrounding undesired strata having different light reflecting properties, is provided. The method comprises the steps of boring in a first direction (horizontally) into the desired stratum with a mining machine, and progressively penetrating the desired stratum with the mining machine while measuring the distance of the mining machine from the undesired strata in a second direction (up) perpendicular to the first direction. The measuring is accomplished by taking advantage of the different light reflecting properties of the desired stratum and the surrounding undesired strata. The direction of boring is controlled based upon the received measurements so that the machine generally stays within the desired stratum. The measuring is accomplished by boring through the desired stratum toward and into the undesired strata in the second direction, to generate chips, and continuously monitoring a property of the chips that is different for the undesired strata chips than for the desired stratum chips--preferably the light reflecting characteristics of the chips. The boring is accomplished by rotating a rotary drill bit with a peripheral speed that is low--i.e., only about 50 feet per minute, compared to the peripheral speed of a cutting head which is high--i.e., about 600 feet per minute--thus resulting in little wear to the drill bit, especially since it only need contact the normally abrasive undesired strata instantaneously.
The apparatus according to the present invention comprises a mining machine having a high speed cutting head, and adapted to penetrate a geological stratum in a first direction (horizontally). Means for penetrating the desired stratum and toward and into the undesired strata in a second direction (up) generally perpendicular to the first direction is also provided, such means preferably comprising a rotary drill mounted on the mining machine posterior of the cutting head. Means are provided for measuring the distance of the mining machine from the undesired strata in the second direction, this being accomplished by utilizing a light source mounted on the machine and a reflective surface and a photocell mounted in operative relationship with the light source, the chips generated during boring in the second direction being contacted by the light emitted from the light source, and reflected to the photocell. An abrupt change in the light reflecting properties of the chips--such as occurs when the undesired stratum is contacted--causes the photocell to change its conductivity, which effects operation through solid state circuitry to automatically stop the advance of the drill and return the drill to its original position. A digital counter counts the extent of penetration of the drill, and the counter displays the distance digitally until the next cycle of operation is begun at which time it automatically resets. Utilizing such apparatus, it is possible to always remain in the desired stratum since advance warning is provided when the boundary of the desired stratum is being reached, and in this way it is possible to leave any desired amount of desired stratum overhead that is necessary for safety purposes.
It is the primary object of the present invention to provide a simple, safe, and efficient method and apparatus for maintaining a mining machine in a desired geological stratum. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.